The mass flow rate of air through the compressor of a gas turbine engine generally varies as a function of the ambient temperature. On hot days, the density of the air may decrease by about ten percent (10%) to about twenty percent (20%) as compared to a standard ISO day (“International Organization for Standardization”) of about 59 degrees Fahrenheit (about 15 degrees Celsius). As such, the overall power produced by the gas turbine engine also may be reduced by about ten percent (10%) to about twenty percent (20%) or so. This reduction in output, however, generally coincides with higher consumer and industrial power demands due to increased air conditioning loads and the like. As a result, the combination of elevated power demands and reduced generation capacity may elevate power prices by a multiple of ten or more as compared to normal power demands and capacity during a lower temperature day.
Attempts to increase power generation on hot days have included increasing the size of the compressor to compensate for the lost flow rate. The increased scale, however, also may result in increased costs. Moreover, increased temperatures on warmer days may lead to increased compressor pressures and temperatures. Such increased pressures and temperatures generally require the use of expensive nickel based alloys at least in the aft section of the compressor so as to provide durability against low cycle fatigue. These alloys, however, may be relatively expensive as compared to standard gas turbine components.
Various types of water cooling methods also have been used. For example, inlet fogging about the compressor inlet may reduce the compressor inlet air temperature. Such a reduction in air temperature generally restores the mass flow rate and thus the generated power. Inlet fogging, however, generally is only useful until the wet bulb temperature is reached such that the practice has limited utility on humid days. Wet compression involving a spray of water inside the compressor inlet also has been used. Latent heat for the evaporation of the water cools the inlet air stream so as to increase the power available due to the reduction of work required for compression of the inlet air. The addition of the water stream, however, may have thermal stress and/or erosion issues.
There is thus a desire for an improved compressor and methods of operating the same so as to provide a constant level of power generation across the ambient temperature operating range, particularly on hot days. Such constant power generation would allow power producers to meet power generation requirements during periods of both high demand and hence high profitability. The compressor and methods thus should be temperature flexible while maintaining high levels of efficiency and durability.